1. Field of Invention
The invention relates to rigid films of cycloolefin copolymers, a process for the production of such films and their use, in particular, for the production of thermoformed components.
2. Description of Related Art
Cycloolefin copolymers have the following properties that are advantageous specifically for films:
high transparency (for optical uses) PA1 good dielectric properties (as a capacitor dielectric) PA1 high softening points, in particular, at a high cycloolefin content (for high temperature uses) and PA1 good gas barriers (for uses in the packaging sector).
Films prepared from cycloolefin copolymers are known. DD-A 224 538 and DD-A 241 971 describe cast films of ethylenenorbornene copolymers. EP-A 0 384 694 also describes films of cyclic copolymers. Except for the norbornene copolymers, other cycloolefinic starting materials mentioned therein are comparatively expensive and therefore uneconomical.
One disadvantage of the known cycloolefin copolymer films is that the E modulus, in particular, the tensile E modulus, is too low for the production of extremely thin films. The E modulus has a direct influence on the winding properties of a film. The lower the E modulus, the greater the risk that irreversible extensions occur due to tensile stresses generated during winding of the film.
Some cycloolefin copolymers that may be suitable for the production of the films according to the invention are described in EP-A 0 407 870, EP-A-0 503 422 and in DE-A 40 36 264 the disclosures of which are incorporated by reference herein. These documents also mention that films can be produced from these raw materials. These documents also include, however, many cycloolefin copolymers that are not suitable for the production of films according to the invention since they are too ductile, and an optimum E modulus at the lowest possible film thickness is not achieved. Suitable mechanisms for preparing cycloolefin copolymers having the specific microstructure described below are not described in these documents.